Persons using biocidal agents in the biocidal treatment of water customarily, if not universally, refer to “free chlorine” level as a measure of biocidal control. To achieve “free chlorine” levels in water treatment, solid materials are often preferred because of their high weight percent activity. N,N′-bromochloro-5,5-dimethylhydantoin (BCDMH) has been one of the most widely-used solid sources of “free chlorine” for water treatment. One of the features emphasized for BCDMH by suppliers of BCDMH is that in use, the combined chlorine from the biocide regenerates “free chlorine” by reaction with inactive bromide species formed during the water treatment operation. In other words, the chlorine atom in the initial N,N′-bromochloro-5,5-dialkylhydantoin is said to be a precursor for additional “free chlorine” for sanitation purposes.
While effective, BCDMH does have certain heretofore-unrecognized drawbacks. For example, when used at conventional dosage levels in treating industrial water systems, the rate of corrosion of iron and copper surfaces in contact with the treated water is higher than desired. In addition, the rate of consumption of the BCDMH in treating the water for effective biocidal action is significantly higher than is desirable from the standpoint of the consumer. Further, during usage the amount of halogen residual in the treated water is lower than would be desired.
Further shortcomings of BCDMH are that in use, BCDMH hydrolyzes into HOBr and HOCl both of which register as “free chlorine” species in commonly-used standard test procedures. These methods for determining “free chlorine” levels in treated water, involve use of a reagent known as DPD (i.e., N,N′-diethyldiphenylenediamine) and a buffer, and the results of such analyses are commonly used, if not universally used, as the basis for determining the quantity of a halogen-containing microbiocidal agent to be used for water treatment. Heretofore, consumers of BCDMH have only been concerned with the level of “free chlorine” provided by a given quantity of that biocidal material. What has not been realized by such consumers is the amount of “total chlorine” being utilized in order to achieve the requisite “free chlorine” level. As a consequence, the consumer has not had available a yardstick by which to determine the true economic efficiency of using BCDMH as a biocidal agent in the treatment of water. To achieve optimum economic efficiency, the consumer should have available for use a biocidal agent in which the amount of “free chlorine” released into the water corresponds closely to the “total chlorine” content of the biocidal agent.
In the event a biocidal agent provides a relatively small amount of “free chlorine” in relation to its “total chlorine” content, it has been deemed necessary to utilize a relatively large amount of such agent in order to achieve microbiological control. This in turn means high levels of halogenated materials are released into the environment. If on the other hand, a biocidal agent could provide to the water an amount of “free chlorine” that closely corresponds to the “total chlorine” content of the biocidal agent, effective microbiological control could be realized by use of much smaller dosages and with consequent minimal adverse impact upon the environment.
Also, while reasonably effective as a microbiocide, BCDMH is not as effective against biofilms tested to date as would be desired. Biofilms are bacterial films which tenaciously adhere to surfaces in contact with water such as heat exchanger surfaces, conduit interiors, filters, and other processing equipment. These films are very undesirable because they can harbor dangerous pathogens, and cause damage to the surfaces to which they have become attached. Moreover, the bacteria form a slime layer of extra-cellular polysaccharide which affords protection to the bacteria and in addition constitute an effective barrier against penetration of biocidal agents used in an attempt to combat such bacteria. In situations where the water is prone to development of calcium carbonate scale, the presence of such gelatinous extra-cellular polysaccharides can result in the formation of layers of scale bonded to the substrate surface by the gelatinous polysaccharides. Polysaccharide films and films of scale bonded by means of polysaccharides can greatly interfere with the operation of heat exchangers by virtue of their insulating characteristics, and can markedly interfere with the functioning of filters and the flow of water through pipes and conduits by virtue of the clogging tendencies of such polysaccharide films.
It would therefore be of considerable advantage if these drawbacks could be avoided in actual practice.